Ionomer resin materials are generally used for their durability in golf ball inner cover and outer cover layers. For example, when golf balls include an outer cover layer formed from an ionomeric material, the golf ball provides a good combination of distance and durability. In fact, U.S. Pat. No. 4,431,193 relates to a golf ball having a multilayer cover wherein the inner layer is a hard, high flexural modulus ionomer resin and the outer layer is a soft, low flexural modulus ionomer resin, and wherein either (or both) layer may include a foamed ionomer resin.
But, because ionomer-covered golf balls have a hard “feel” and lower spin rate when struck with a club, golf ball manufacturers typically replace the ionomer cover with a softer cover formed from polyurethane or polyurea. The softness of the polyurethane and polyurea materials can be balanced with a harder inner cover or intermediate layer.
Since the inner cover layer or intermediate layer is intended to provide a degree of stiffness to a soft cover ball, the materials selected must have suitable flexural modulus values. As such, ionomer resins are generally used to form at least a part of the inner cover layer or intermediate layer in a soft cover golf ball. To date, however, commercially available ionomer resins do not have a flexural modulus greater than 70,000 psi measured after 2 weeks with 4-point blending. For example, SURLYN® 8940, 9650, and 9910 have flexural modulus values of 51,000 psi, 32,000 psi, and 48,000 psi, respectively.
Thus, it would be advantageous to produce a composition that provides improved stiffness to an inner cover layer or intermediate layer for use with a soft cover golf ball to provide reduced spin rate off the driver to increase distance. In particular, there exists a need for golf ball layer compositions that have hard, high flexural modulus values, i.e., values greater than that which is commercially available. The present invention provides a composition with higher flexural modulus values to provide a greater degree of stiffness to the golf ball.